Method of tube drawing



3 Sheets-Sheet 1 INVENTOR 176L 11 TORNEYS- Oct. 7, 1947. A. J. SNIVELYMETHOD OF TUBE DRAWING Filed March 27, 1944 Oct. 7, I947. A. J. SNNELY2,428,474

METHOD OF TUBE DRAWING Filed March 27, 1944 3 Sheets-Sheet 2 I INVENTORAndrew 5/7/ ve/y ATTORNEYJi Oct. 7, 1947. A. J. SNlVELY 2,428,474

METHOD OF TUBE DRAWING Filed March 27, 1944 3 Sheets-Sheet 5 Fiqll.Fnrla.

INVENTOR AfldrewJJn/Ve(y Patented O ct. 7, 1947 METHOD OF TUBE DRAWINGAndrew J. Sniveiy, Huntington Woods, Mich., as-

signor to Bundy Tubing Company, Detroit, Mich., a corporation ofMichigan Application March 27, 1944, Serial No. 528,312-

9 Claims. (Cl. 205-8) 1 This invention relates to the drawing of tubingand it has to do particularly with a type of draw wherein the wall ofthe tube is thinned and the tube elongated.

The invention is directed particularly to the art of drawing wherein thetube, throughout its length, is drawn down upon a mandrel which is atleast as long as the tube. In such a procedure, the tube, at thebeginning of the process, is relatively short and the mandrel relativelylong. The tube and mandrel are pulled through adie so that the tube wallis reduced in thickness and the tube extended, the tube being drawn downtightly upon the mandrel. Heretofore several passes of the tube andmandrel were required in a single drawing action; thus the tube wasdrawn down tightly against the mandrel and subsequently one or morepasses were required through means for loosening the tube from themandrel. The tube must be loosened from the mandrel if it is to beremoved therefrom and it must be loosened from the mandrel if asubsequent drawing pass is to be made in order to permit the elongationof the tube relative to the mandrel.

Heretofore, in this type of mandrel drawing, the leading end of themandrel was considerably tapered or reduced in section and the leadingend of the tube was reduced upon the leading end of the mandrel, so thatthe two could be passed into the draw die. The pulling instrument wasapplied to the tube and mandrel so that both the tube and the mandrelwere pulled. The taper or reduction of the leading end of the mandrelweakened it and shortened the mandrel life. Moreover this arrangementalso required additional operations to loosen the tube from the reducedand roughened leading end of the mandrel- The general object of theinvention is to provide improvements in the tube drawing art so that ina single pass, the tube is drawn upon the mandrel and then loosened fromthe mandrel so that the tube and mandrel are ready for a subsequent drawor can be readily separated if there is no subsequent draw. In thisconnection, a novel manner of pulling the tube through the drawingandloosening mechanism is provided wherein only the mandrel is subjected tothe pulling action of the draw bench and the tube is pulled by reason ofthe frictional engagement between the tube and mandrel which engagementis caused by the die forcing the wall of the tube against the mandrel.In other words the mandrel pulls the tube by reason of the frictiontherewith. This, of course, sets up a problem of starting the drawingaction because the tube is initially and necessarily loose on themandrel. Accordingly, the invention provides a novel manner of startingthe draw to initially set up the frictional engagement between themandrel and the tube. Inasmuch as the mandrel is under a substantial.tension during the drawing action, it may be damaged or buckled when thetrailing end of the tube leaves the drawing die because of the suddenrelease of the tension. The invention provides for a gradual reductionof this tension adjacent the trailing end of the tube so that the finalrelease when the trailing end of the tube leaves the die is not such asevere action as to cause damage to the mandrel or other parts. Inaccordance with the invention one or more draw passes may be employed,depending upon the desires and objects to :be obtained, and of coursedepending also upon the type of metal of which the tube is formed.

The accompanying drawings illustrate the method and one form ofapparatus for carrying out the invention. In these drawings:

Fig. 1 is a view illustrating diagrammatically an apparatus for drawingtube in accordance with the present invention,

Fig. 2 is a view illustrating the base tube on the mandrel prior to thefirst draw.

Fig. 3 is a view similar to Fig. 2, showing the tube on its mandrelfollowing the first draw.

Fig. 4 is a view illustrating the tube and its mandrel following thesecond draw.

Fig. 5 is a view illustrating the head containing the draw die, a set ofpinching rolls and the loosening die.

Fig. 6 is a cross sectional view taken on line 66 of Fig. 1 showing someof the pinching rolls.

Fig. 7 is a sectional view taken online 1-1 of Fig. 1 showing otherpinching rolls.

Fig. 8 is a sectional view through the draw die, showing the tube andmandrel at the start of a draw and before the tube has entered the die.

Fig.9 is a view similar to Fig. 8 showing the tube as its leading endhas passed into the die.

Fig. 10 is a sectional view similar to Figs. 8 and 9, illustrating thedrawing action after it is well started.

Fig. 11 is a cross sectional view taken substantially on line ll-il ofFig. 1 showing the base tube and the mandrel prior to the drawingaction.

Fig. 12 is a cross sectional view taken substantially on line i2l2 ofFig. 1 showing the tube and mandrel down stream from the draw die.

Fig. 13 is a sectional view taken substantially on line l3-i3 oi Fig. 1showing the results of the first group of pinching rolls.

Fig. 14 is a sectional view taken substantially bench i equipped with apulling device at 2 or conventional construction. On the bench is a drawdie 3 provided with a suitable passage and on the up stream side 01which is a suitable container of lubricant through which the tubepasses.

The mandrel is illustrated at 8 and it has a length at least as great asand preferably greater than the length of the finished tube. Thismandrel is preferably of the so-called piano wire or the like, having ahigh tensile strength and its leading end i is reduced in size where itis to be gripped by the puller 2. The purpose of reducing the leadingend is so that the surfaces of the mandrel which become roughened orburred by the gripper 2 will not cut or scratch the interior of the tubewhen the mandrel is inserted therein. The tube I is passed over themandrel and the base tube and mandrel prior to any drawing action mayappear as substantially shown in Fig. 2.

Inasmuch as the puller 2 is applied only to the mandrel, means arerequired to enter the leading end of the tube into the die. To this endthe leading end of the tube has its wall section weakened as by beingthinned or reduced in cross section. As shown in Fig. 8, the leadingendof the tube is provided with an internal tapering formation which thinsthe tube ,wall. This thinning may be done by subjecting the leading endof the tube to a swaging action or by machining or grinding the same.

internally. Also the trailing end ofthe tube is similarly treated asshown in Fig. 16 where the trailing end of the tube wall is reduced asshown at I2.

To start a draw, the tube is first passed over the mandrel and then theleading end of the 1 mandrel is passed through the die as shown in Fig.8 and through the pinching rolls, the loosening die and the wiper 31.The puller 2 is now applied to the leading end of the mandrel and thepulling action started. It will be observed .that in the absence of anyconnection between suitable gripping device similar to a large pair ofpliers. The jaws l3 and M of the gripper are applied to the mandrel andcome into an abut- This forces the leading end of the tube into the die,this actionbeing facilitated because of the It is within the inventionto reduce the leading end externally as well as the drawing process isin operation, the die. tube ting relation with the trailing end of thetube.

weakened nature of the leading end of the tube caused by the thinning ofthe walls. After the leading end of the tube has passed into the die, itis forced down tightly upon the mandrel and when the frictional contactbetween the tube and mandrel-is of sufficient length and the connectionstrong enough to pull the tube with the mandrel the plier jaws l3 and Mare removed. The plier jaws l3 and it may be applied by hand. After andmandrel may appear as shown in Fig. 10. It must be pointed out, however.that the leading. end of the mandrel at the beginning of a drawoperation is not only threaded through the die but also passed throughthe pinchin and loosening die structures as shown in Figs. 1 and 5.

.The pinching rolls for treating the tube wall preparatory to looseningthe wall from the mandrel are located down stream from the die as shownin Fig. 1. An advantageous construction is to employ a set or pinchingrolls arranged in two groups of 4. One group as shown in Fig. 6 has 4rolls each indicated at is with the rolls arranged at right angles toeach other. The rolls may be idling rolls and are beveled adjacent theirperipheries to provide a clearance relative to each other. Two of therolls are applied to the tube by. hydraulic pressure through the meansof the cylinder and piston structures ll while the 0pposing two are infixed position although capable of adjustment by the nuts IS on thethreaded posts as indicated. This adjustment permits of adjusting therolls for difierent size tubes and also for adjusting the rolls toaproper central position.

As shown in Fig. 7 there is a second group of pinch rolls each indicatedat 28. These rolls may be identical with the first group of'rolls butare disposed at 45 degrees relative to the rolls of the first group. Twoof these rolls may be applied to the tube by hydraulic pressure asindicated by the cylinder and piston structures it while the opposingtwo are adjustably fixed as, at 22. A suitable lubricant may be appliedto the tube between the draw die and the pinch rolls as indicated by alubricant supply pipe 25 for discharging the lubricant directly on thetube.

Pinching rolls of this typehave been termed Turk's head" rolls and theirfunction is to flow the metal of the tube circumferentially with someresultant thinning of the tube wall so that the tube may be loosenedfrom the mandrel. This function is illustrated in Figs. 13 and 14. InFig. 12 of course the tube is very tightly applied to the mandrel. Infact the grip between the tube and the mandrel is so strong that it isemployed as a. pulling agency to pull the tube through the drawing die.The first group of rollers I6 apply pressure to the tube at locationsspaced degrees apart and this thins the wall somewhat as illustrated at30 and causes the metal to flow and bulge between. the locations ofroller contact as illustrated at 3 I. Thus the metal at the four 10-cations 3i is forced away from and out of contact with the mandrel 6 asillustrated. The next group of rollers 20 engage the tube at bulgedportions 3i and thin the metal somewhat as at am so as to cause a flowaction with the result that the metal between the locations of contactby the rollers is bulged away from the mandrel as indicated at 30a. Itwill be seen with reference to Fig. 14 that a considerable spacing isprovided between the mandrel and the portions 30a as illustrated at-32.Thus the circumferential extent of the tube wall is increased. In otherwords, the interior periphery of the tube is enlarged over thecircumference of the mandrel. At this point, however, the tube is stilltightly applied to the mandrel particularly at locations 3la. To freethe tube from the maximum cross dimension or the tube in the form asshown in Fig. 14 and greater than the diameter of the mandrel plus twicethe wall thickness of the tube at this point. The rather squaredrormation of the tube wall is thus brought back into rounded conditionas shown in Fig. 15, with the tube wall thinned and enlarged over itscondition as shown in Fig. 12 and thus loose on the mandrel as indicatedby the spacing at 39. Down stream from the rounding die a wiper 31 ispreferably disposed, particularly for the purpose of wiping the trailingend of the mandrel as it is drawn therethrough to facilitate asubsequent draw.

It will be appreciated that the mandrel is under a substantial tensionand if this tension were suddenly released as the trailing end of thetube passed out of the draw die 3,'the resultant shock and snap actionmight bend the mandrel and even cause damage to other parts. To meetthis situation, the trailing end of the tube, as shown in Fig. 16, isgradually thinned or tapered so that the tension gradually reduces andthe resultant shock and snap when the end of the tube leaves the drawdie is minimized.

As illustrated in Fig. 5, the draw die, Turks head" rolls and roundingdie may all be constructed as a compact unit assembly. Where the tube isto be given more than one draw as, for example, 2 draws, the mandrel andtube may appear relatively as indicated in Fig. 3 following the firstdraw pass. In this condition the tube is loose on the mandrel as shownin Fig, 15. This is necessary because in a subsequent draw, the tube isgoing to elongate on the mandrel to a condition as exemplified in Fig.4. With the mandrel and tube in the condition as shown in Fig. 3 theymay be again pulled through a drawing mechanism identical with the onedescribed above including the draw die, "Turks head rollers and roundingdie except for diameter size. To start the second or any draw subsequentt the first, the tube wall may be collapsed as by means of a toolsimilar to a pair of pliers with its jaw 40 and 4| applied to the tubewith pressure. This causes a frictional engagement between the mandreland the tube and as the mandrel is pulled through a draw die of asubsequent draw action, the leading end of the tube is pushed throughthe draw die by the friction caused by the jaws 40 and 4|. It will beunderstood of course that since the tube wall has been thinned by thefirst draw that it is not so difficult to cause the leading end of thetube to enter the die of a second draw.

The number of rollers used in the Turks head structure is of coursesubject to variation. Eight rollers are shown herein divided into twogroups of 4. The larger the number of rollers usedthe less the variationin the wall thickness of the completed tube. Where a tube is requiredwith an extremely accurate exterior surface the drawn tube may be passedthrough a sinking die to smooth and round the finished tube. In such acase the tube is preferably annealed before sinking.

Thus it will be observed that in a single pass the tube is drawn uponthe mandrel and it is loosened from the mandrel so that the tube andmandrel I may be separated or so that they are conditioned for asubsequent draw. The tightness with which the tube engages the mandrelmay be appreciated when it is considered that the portion of the tubewhich tightly engages the mandrel for pulling purposes lies principallybetween the drawing die and the first group of "Turks head, rollers.This may be only a matter of a few inches.

The draw which may be eflected with this arrangement is severe andtherefore a substantial tubewall reduction can be had with a minimumnumber of passes. To exemplify this, anexample is herewith given or thedrawing of a tube made 01' 1010 steel, ordinarily called low carbonsteel,

it being understood of course that the invention is not limited to thisexample. In this example, the base tube had an original outside diameterof .375 in.; its well was .028 in. thick; its interior diameter .319in.; the mandrel had a diameter of .306 in. At this point it may bepointed out that some latitude is permissible in the clearance betweenthe mandrel diameter and the interior diameter of the base tube. Theinterior diameter or the draw die was .327 in.; the base tube was 5 /2ft. in length while the mandrel was 30 it. long and draw bench 32 it.long. Following the first draw, the outside of the diameter of the tubewas .331 in.; its wall thickness was .0105 in. in thickness; itsinterior diameter .309 to .310 in. It will be observed that the interiordiameter following the first draw was about .003 to .004 in. greaterthan the diameter of the mandrel and that the outside diameter was about.004 in. greater than the inside diameter of the die. This representsthe enlargement of the tube effected by the pinch rollers and therounding die representing a clearance of about .002 in. at 36 in Fig.15. Following this draw, the tube had been extended to about 16 ft. inlength as indicated at Fig. 2. On the next draw the interior diameter orthe draw die was .318 in.; following the second draw pass the outside ofthe tube was .322 in.; the wall thickness was .006 in.; the insidediameter was about from .309 to .310 in. Here again it will be notedthat the outside diameter of the tube following the second draw pass isabout .004 in. greater than the inside diameter of the die and that theinside diameter of the tube remained the same as it was following thefirst draw pass or namely, about .309 in, to .310 in. Following thesecond draw, the length of the tube was about 28 ft. as represented inFig. 4. In the above example, no attempt has been made to show anydimensional variations in the intermediate conditions as shown in Figs.12, 13 and 14.

It will be observed that with two draw passes, there is a substantialreduction in the thickness of the tube wall and a substantial elongationof the tube. The amount of draw or metal flow obtainable in a pass maybe varied, as this depends largely upon the nature and ductility of themetal of the tube. Following the first draw, the tube is loose upon themandrel and can be removed if this is the total amount of reductiondesired. The looseness of the tube as pointed out above, is necessaryfor a subsequent pass through the draw die because of the elongation ofthe tube. In this connection, the wiping of lubricant from the trailingend of the mandrel by wiper 31 is important.. If there is too muchlubricant on the trailing end of the mandrel during the second draw,which start with the condition as shown in Fig. 2, where the tube wallhas been substantially reduced in thickness, this lubricant passes intothe tube around the mandrel as the mandrel is pulled through the die andas the tube elongates. The result is the building up of a hydraulicpressure within the already thinned tube and the pressures therein maybecome so great as to break or rupture the tube wall. Only a thin filmof lubricant is needed between the tube and mandrel because the relativeaxial movement occurs where the mandrel is loose within thetube. Afterthe tube is drawn down upon the mandrel there is no further relativemovement between" the tube and mandrel.

, I claim:

1. In the method of drawing tube wherein a mandrel is placed within thetube and the tube and mandrel ar e moved through a die so that the tubewall is reduced in thicknes between the die and mandrel; the steps ofapplying pulling forces directly to and only to the mandrel, therebycausing the mandrel to move relative to the die, feeding the tub intothe die to cause its wall to be forced into frictional engagement withthe mandrel, discontinuing the feeding of the tube and pulling the tubethrough the die by the means of frictional engagement of thetube-withthe mandrel.

2. In the method of drawing tube wherein a mandrel is placed within thetube and the tube and mandrel are moved through a die so that the tubewall is reduced in thickness between the die and mandrel; the steps ofplacing the tube over the mandrel in loose and otherwise unattachedrelationship, applying pulling forces directly to the mandrel to causethe mandrel to move relative to the die, feeding the tube to cause itsleading end to enter the die so that the wall of the tube is forced intofrictional engagement with the mandrel, discontinuing the feeding of thetube and thereafter pulling the tube through the die by means of thefrictional engagement of the tube with the mandrel.

3. In the method of drawing tube wherein a mandrel is placed within thetube and the tube and mandrel are moved through a die so that the tubewali is reduced in thickness between the die and mandrel; the steps ofweakening the leading end of the tube, placing the tube on the mandrelin loose and otherwise unattached relation-= ship, pulling the mandrelrelative to the die, feeding the leading end of the tube into the dieso'that it is forced into frictional engagement with the mandrel,discontinuing the feeding of the tube and pulling the tube through thedie by the means of its frictional engagement with the mandrel.

4. In the method of drawing tube wherein a mandrel is placed within thetube and the tube and mandrel are moved through a die so that the tubewall is reduced in thickness between the die and mandrel; weakening boththe leading and trailing ends of the tube, placing the tube over themandrel, pulling the mandrel to cause it to move relative to the die,feeding the leading end of the tube into the die to cause its wall to beforced into engagement with the mandrel, discontinuing feeding of thetube and pulling the tube through the die by means of frictionalengagement of the tube with the mandrel, the weakening of the trailingend of the tube serving to gradually reduce the tension on the mandrelto reduce the shock when the trailing'end of the tube passes through thedie.

5. In the method of the drawing tube wherein a mandrel is placed withinthe tube and the tube and mandrel are moved through a die so that thetube wall is reduced in thickness between the die and mandrel;treatingthe leading end of the tube to give'its wall a, tapering form,placing the tube over the mandrel in loose and otherwise unattachedrelationship, applying pulling forces to the mandrelto cause the mandrelto move relative to the die, feeding the tube into the die to cause itsleading end to be forced into frictional engagement with the mandrel,discontinuing the feeding of the tube and pulling the tube through thedie by means of the frictional engagement of the tube with the mandrel.

6. In the method of drawing tube wherein a mandrel is placed within thetube and the tube and mandrel are moved through a die so that the tubewall is reduced'in thickness between the die and mandrel; treating theleading end of the tube to give its wall a tapering form, similarlytreating the trailing end of the tube, placing the tube over themandrel, applying pulling forces to the mandrel to cause the mandrel tomove relative to the die, feeding the tube into the die to cause itsleading end to be forced into frictional engagement with the mandrel,discontinuing the feeding of the tube and pulling the tube through thedie by means of the frictional engagement of the tube with the mandrel,the tapering section at the trailing end'of the tube serving togradually reduce the tension of the mandrel to reduce the shock of therelease when the trailing end of the tube moves through the die. I

7. In the method of drawing tube wherein a mandrel is placed within thetube and the tube and mandrel are moved through a die so that the tubewall is reduced in thickness between the die and mandrel; the steps ofplacing the tube over the mandrel in loose and otherwise unattachedrelationship, inserting the leading end of the mandrel through adraw'die and loosening mechanism, pulling the mandrel lengthwise,feeding the tube into the draw die to cause it to be forced intofrictional engagement with the mandrel, discontinuing the feeding of thetube and" pulling the tube through the draw die by means of thefrictional engagement of the tube with the mandrel and then through theloosening mechanism to loosen the tube on the mandrel.

8. In the method of drawing tube wherein a mandrel is placed within thetube and the tube and mandrel are moved through a die so that the tubewall is reduced in thickness between the die and the mandrel; the stepsof placing the tube over the mandrel in loose and otherwise unattachedrelationship, applying pulling forces to the mandrel to cause themandrel to move relative to the die, applying force to the tube to causeits leading end to enter the die so that the wall of the tube is forcedinto frictional engagement with the mandrel to thereby establish thesole connection between the tube and the mandrel, discontinuing theapplication of force to the tube and pulling the tube through the die bymeans of the frictional engagement of the tube with the mandrel.

9. In the method of drawing tube wherein a mandrel is placed within thetube and the tube and mandrel are moved through a die so that the tubewall is'reduced in thickness between the die and the mandrel; the stepsof placing the tube over the mandrel in loose and otherwise unattachedrelationship, applying pulling forces to the mandrel to cause themandrel to move relative to the die, weakening the leading end of thetube so that it may be relatively easily ensmalled by the die, applyingforce to the tube to cause its leading end to enter the dieso that thewall of the tube is forced into frictional engagement with the mandrelto thereby establish the sole connection of force to the tube andpulling the tube through the die by means of the tric- Name I Date IEngelbertz June 15, 1937 Ivins Aug. 16, 1898 Von Forster Nov. 22, 1932Linderme June 9, 1925 FOREIGN PATENTS Country Date Great Britain Mar. 8,1902 Great Britain Nov. 25, 1867 Germany Nov. 1, 1930

